Within the oil & gas industry, well operators need to quantify the efficacy of hydraulic fracturing treatments performed on their wells in order to optimize production. The current standard practice is to inject radioactive tracer materials into the fractures and run a standard gamma ray log. Gamma ray logs are known in the art for measuring the background level of radioactive materials in a formation during the exploration or drilling phase of a well in order to aid in identification of the formation rock type and estimate hydrocarbon reserves. When used during hydraulic fracturing evaluation, the gamma ray logging tool registers elevated gamma ray levels at the depths of fractures into which the radioactive tracer material was injected. This can tell an operator where open fractures are located axially along the well bore but cannot give any information about where open fractures are located azimuthally around the well bore or the depth of the fractures.
No viable technologies are currently available that use a method or means to employ at least one collimated detector located within a borehole logging tool to produce three-dimensional images and maps of the location and depth of formation fractures filled with radioactive material within a cased borehole.
Prior art teaches a variety of techniques that use gamma ray logging techniques to locate the fractures and estimate the fracture depth, but none can produce a three-dimensional image of the fractures.
US20180188411 to Teague et al. teaches methods and means for improving the resolution and determination of the density of the materials surrounding a wellbore, in a package requiring no direct physical contact with the well casings (i.e., non-padded). The method and means described herein comprise using an actuated combination of collimators located cylindrically around an x-ray source, the actuated combination of collimators being located within a non-padded concentrically-located borehole logging tool, for detecting density variations within the annular materials surrounding a borehole within single or multi-string cased-hole environments. The actuation of collimators permits the operator to choose between a fixed collimator mode in which the output is an azimuthal array of a plurality of x-ray beams, and an actuated collimator mode in which a single or plurality of individual azimuthally-arranged x-ray beams scan azimuthally through the rotation of one of the collimators. In addition, the actuation permits the operator to select a further non-rotating-mode in which the collimator sleeve switches among various angles or declinations of x-ray beam outputs with respect to the major axis of the tool.
U.S. Pat. No. 7,705,294 to Teague teaches an apparatus that measures backscattered x-rays from the inner layers of a borehole in selected radial directions with the missing segment data being populated through movement of the apparatus through the borehole. The apparatus permits generation of data for a two-dimensional reconstruction of the well or borehole.
U.S. Pat. No. 9,817,152 to Sofiienko et al. teaches a method and means of creating a three-dimensional map of cement, casings and formation surrounding a cased borehole, using x-ray radiation to illuminate the casings, annular materials and formation. Further, it teaches a means that produces a voxelated map that contains axial, radial and azimuthal density variations, and thereby the geometry and form of the cement surrounding the cased hole.
U.S. Pat. No. 4,439,677 to Martin discloses a method for determining the vertical extent of a fracture in a wellbore injecting radioactive tracers along with a filter cake material into a well. When the filter cake forms at the entrance to each fracture, the radioactive material will be stuck in the filter cake and a nuclear log survey can detect that radioactive material to determine the height of the fracture.
U.S. Pat. No. 4,415,805 to Fertl et al. discloses a method for evaluating a multistage fracturing operation by injecting a different radioactive tracer with each stage of the fracture operation. By separating the gamma ray log signals according to the characteristic energies of each different tracer, the efficacy of each stage can be assessed separately.
U.S. Pat. No. 4,464,569 to Flaum discloses a method for determining the elemental composition of earth formations surrounding a well borehole by processing detected neutron capture gamma radiation emanating from the earth formation after neutron irradiation of the earth formation by a neutron spectroscopy logging tool.
U.S. Pat. No. 4,433,240 to Seeman discloses a borehole logging tool that detects natural radiation from the rock of the formation and logs said information so that it may be represented in an intensity versus depth plot format.
U.S. Pat. No. 4,825,073 to Smith et al. discloses a method for determining the depth of penetration of a formation fracture by injecting radioactive material into the fracture and then detecting the emitted radiation in two energy ranges. The ratio of the intensity of detected radiation in a higher energy range where the radiation has not undergone Compton scattering to that in a lower energy range where the radiation has undergone Compton scattering indicates the depth into the formation at which the radiation originated and can be used to estimate the depth of the fracture.
U.S. Pat. No. 4,857,729 to Gadeken et al. discloses a method for radioactive well logging in which radioactive isotopes are used to tag the hydraulic fracturing material. A low energy radioisotope is chosen for the fluid and a high energy radioisotope is chosen for the solid within the hydraulic fracturing mixture. The radiation detected from the two separate isotopes can be used to correct for the effects of radioactive material within the wellbore.
U.S. Pat. No. 4,926,940 to Stromswold discloses a method mapping fractures involving injecting a neutron-activated radioactive material into the fractures. Logging the well before and after fracturing gives a measure of the extent of the fractures.
U.S. Pat. No. 5,322,126 to Scott discloses a method of actively monitoring fracture growth during a hydraulic fracturing operation by injecting neutron-activated radioactive material with the fracturing fluid, activating the material by passing next to a neutron source as the fluid travels into the well, and sensing the emitted radiation from the activated material in the fracture using multiple sodium-iodide scintillometer detectors.
U.S. Pat. No. 5,410,152 to Gadeken discloses a method of obtaining fracture penetration depth by measuring the radiation emitted by radioactive tracers injected into fractures across multiple energy bins. Then, the signals from different energy bins are correlated with the depth into the formation from which each signal arose.
U.S. Pat. No. 5,441,110 to Scott discloses a method of actively monitoring fracture growth during a hydraulic fracturing operation by injecting gamma-emitting tracer material into the fracture fluid using downhole-placed exploding charges, and sensing the emitted radiation from the material in the fracture using multiple sodium-iodide scintillometer detectors.
U.S. Pat. No. 5,442,173 to Wraight discloses a method of monitoring formation fracturing in real-time by means of injecting fracture fluid containing radioactive isotopes and placing detectors at pre-determined positions in the wellbore. An increase in the signal received by these detectors means that the fracture fluid is approaching the height or vertical depth of the detectors. Once the desired level is reached pumping of fracture fluid can be stopped.
U.S. Pat. No. 5,635,712 to Scott discloses a method of actively monitoring fracture growth during a hydraulic fracturing operation by injecting gamma-emitting tracer material into the fracture fluid using a downhole injector, and sensing the emitted radiation from the material in the fracture using multiple sodium-iodide scintillometer detectors.
U.S. Pat. No. 7,726,397 to McDaniel et al. discloses a method of placing a fracturing fluid or proppant containing vanadium and/or indium into a fracture, activating it with neutrons, measuring the gamma-radiation emitted from the material in a single pass and determining formation fracture height from this single pass.
U.S. Pat. Nos. 7,933,718 and 8,392,120 to McDaniel et al. disclose a method and tool for determining fracture geometry based on in-situ neutron activation analysis. The method involves measuring gamma-radiation emitted from the fracture; subtracting background radiation from the measured gamma-radiation to obtain a peak-energy measurement; comparing the peak-energy measurement with a gamma-ray transport/spectrometer response model; and determining formation fracture geometry of the fracture.
U.S. Pat. Nos. 8,129,318 and 9,243,491 to McDaniel et al. disclose a method of placing a fracturing fluid or proppant containing vanadium and/or indium into a fracture, activating it with neutrons, measuring the gamma-radiation emitted from the material in a single pass and determining formation fracture height from this single pass.
U.S. Pat. No. 9,012,836 to Wilson et al. discloses a method and means for creating azimuthal neutron porosity images in a wireline environment. Similar to U.S. Pat. No. 8,664,587, this reference discusses an arrangement of azimuthally static detectors that could be implemented in a wireline tool to assist an operator in interpreting logs post-fracking by subdividing the neutron detectors into a plurality of azimuthally arranged detectors shielded within a moderator so as to infer directionality to incident neutrons and gamma.
U.S. Pat. No. 4,883,956 to Manente et al. discloses an apparatus and method for investigating subsurface earth formations, using an apparatus adapted for movement through a borehole. Depending upon the formation characteristic or characteristics to be measured, the apparatus may include a natural or artificial radiation source for irradiating the formations with penetrating radiation such as gamma rays, x-rays or neutrons. The light produced by a scintillator in response to detected radiation is used to generate a signal representative of at least one characteristic of the radiation and this signal is recorded.
U.S. Pat. No. 6,078,867 to Plumb discloses a method for generating a three-dimensional graphical representation of a borehole, comprising the steps of: receiving caliper data relating to the borehole, generating a three-dimensional wire mesh model of the borehole from the caliper data, and color mapping the three-dimensional wire mesh model from the caliper data based on either borehole form, rugosity and/or lithology.